Sensation and Perception – PPT - numerons · PDF fileSensation and perception . ......
Transcript of Sensation and Perception – PPT - numerons · PDF fileSensation and perception . ......
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Sensation and perception
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Sensory psychology
• How we know about the world • General principles
– Transduction • receptors
– Adequate stimulus – Law of specific nerve energies
• Battery experiment
– Physical properties give rise to perceptual features • Color is NOT a property of light
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Physical versus perceptual characteristics
• Need to determine relationship between physical and perceptual characteristics
• Vision – light travels in waves – Definition of wavelength
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Wave characteristic of light
Differences in wavelength are perceived as differences in color
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Wave characteristic of light
A and B have same wavelength
B has higher amplitude
Differences in amplitude are perceived as differences in brightness
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Relationship between physical and perceptual characteristics of light
Physical feature How it is perceived
Wavelength Color
Amplitude Brightness
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Visual transduction
• Cornea – Light enters eye
• Pupil – Contraction and
dilation • Iris
– Pigmented part • Lens
– Focuses light on retina
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Visual transduction
• Optic disc – How to find
your blind spot • Retina
– Photoreceptors • Rods • Cones
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Rods and cones
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Visual transduction
• Photochemicals in rods and cones respond to light – Fire action potential – Are carrots really good for your eyes?
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Properties of rods and cones
• Cones (about 7 million in each retina) – Respond best to bright light – Respond to color – Difficult to see color in dark
• Rods (about 120 million in each retina)
– Respond best to dim illumination – Do not respond to color
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From retina to perception
• Optic nerve • Occipital lobe • Feature detectors in the brain
– Respond (fire action potential) only for very specific stimuli
• Some will fire if see horizontal but not vertical line • Some will fire if see “L” but not for straight line
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Perception of letter “t”
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Summary of visual transduction
• Adequate stimulus for vision is light • Enters the eye and is focused on retina • Retina has receptors (neurons) with
photochemicals • Fire action potential when exposed to light • AP to occipital lobe via optic nerve
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Color perception
• Not in the stimulus – Species differences – No brain; no color – Different brain; different color
• Question: What processes give PERCEPTION of color?
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The spectrum of light
• White light combination of all colors • ROYGBIV
– Longest to shortest wavelenths • Red, orange, yellow, green, blue, indigo, violet • Infrared and ultraviolet
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Theories of color vision
• Do not know exactly how perceive color • Trichromatic theory (Young-Helmholtz)
– Found three different kinds of cones – Each has different photochemical – 3 different photochemicals respond best to 3 primary
colors (red, green blue) – Any color can be made from combination of primary
colors
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Trichromatic theory of color vision
• Show a color (pink) – All three cones types respond (fire) – Cone type most responsive to red fires most – Cone types most responsive to green and blue fire less – INTERPRETATION of pattern is pink
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Examples of color perception
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Trichromatic theory and color blindness
• How does color blindness result according to theory?
• Selective color blindness
• Problems for the trichromatic theory – After images
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The opponent process theory
• Photochemicals in cones arranged in opposed pairs – Red-Green – Blue-Yellow – Black – White
• Colors oppose one another
– When see red prevents from seeing green
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The opponent process theory
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Opponent process theory
• Explanation for after images
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Factors affecting color blindness
• Gender
• Race
• Age
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Hearing
• General questions same as for vision (and all other senses) – What is adequate stimulus ? – How does adequate stimulus get transduced (cause
action potential) – Physical properties map on to perceptual characteristics
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Adequate stimulus
• Changes in air pressure • Tuning fork example • Compression and expansion of air molecules
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Physical properties of sound
• Changes in air pressure can be fast or slow – Many or few cycles (compression-expansion) per
second (Hertz –Hz) – Frequency
• Air pressure changes can be high or low
– Amplitude – Measured in decibels (after AGB)
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Physical and perceptual properties of sound
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Relationship between physical and perceptual features
Physical property Perceptual property
Frequency – cycles per second (Hz)
Pitch
Amplitude – decibels Loudness
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Different pitches
200 Hz 2000 Hz
10,000 (10 kHz)
16,000 Hz
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Species differences in perceiving frequencies
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Changes in loudness
Base sound 10 dB louder 20 dB louder
30 dB louder
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How to buy stereo speakers Frequency response
020406080
10050
0
500
1000
5000
1000
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1500
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Frequency
Am
plitu
de $400 $1,000 $5,000
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Decibel value of some sounds
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Pinna
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The outer ear
• Pinna • External auditory canal
Pinna
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The middle ear
• Tympanic membrane (ear drum) • Ossicles – hammer, anvil and stirrup
Pinna
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The inner ear
• The cochlea- filled with fluid not air – Basilar membrane – Hair cells on the basilar membrane
Pinna
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Hair cells
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Transduction in the auditory system
• Changes in air pressure enter the external auditory canal
• Vibrate the tympanic membrane • Vibrate the ossicles • Ossicles “bang” on the cochlea
– Movement of fluid in cochlea – Bending of hair cells
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The process of auditory transduction
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Hearing without hair cells
• Cochlear implants – Electrodes implanted in cochlear next to auditory nerve – Microphone (on belt) receives sound and transmits to
electrodes – Electrodes directly stimulate the auditory nerve
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Cochlear implants
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Cochlear implants
• What do they sound like?
Implant Normal
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Cochlear implants
• Who should get them • Potential disadvantages
• Controversy in deaf community
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Factors that can affect hearing
• Things that can’t control – Age – Gender
• Things that can control – Noise
• Duration and amplitude both important – Frequency
• What frequencies important for speech • What frequencies noise damages • Environmental noise vs. loud music • “walkman” phenomenon
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Damaged hair cells
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Age and hair cell damage
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The “minor” senses
• Smell, taste, and touch • Are they really minor
– Which sense would you LEAST like to lose
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Smell and taste
• Both chemical senses – Adequate stimulus is specific chemical compound
• Smell – Transducers are receptors in nasal passage – Respond only to specific shape of chemical compounds
• Taste – Transducers are taste buds on tongue – Respond to 4 primary sensations
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Tastes are interpreted
• Overall taste determined by combinations of firing of taste buds
• Taste after effects – Similar to visual after effects
• Due to fatiguing of specific taste buds
• Drink distilled water after very sweet water • Orange juice immediately after brushing teeth
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Age and taste
• Very young – Prefer very sweet foods
• Older adults
– Lose sensitivity to sweets – Many no longer like chocolate
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Smell
• Receptors in nasal passages respond to specific chemicals
• Humans relatively poor at identifying smells • Large gender differences • Males better at identifying
– Musk – active ingredient in most perfumes – Brut after aftershave
• Females better at – Juicy fruit gum, coconut, and prune juice
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Pheromones
• What are they? • Importance in other species • Importance in humans?
– Coordination of menstrual cycles in women living together?
– Males 100,00 times more sensitive to musk than women
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Perception
• Difference between sensation and perception – Receptors transduce information (sensation) – Brain interprets that information (perception)
• Prosopagnosia – inability to recognize familiar
faces – Can identify facial features (nose, eyes, etc.) – Can’t recognize as “Bob”
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Depth perception
• Should we see in depth? – Image on retina
• Binocular disparity • Demonstration
– while holding finger near nose alternate blinking – Move finger to arm’s length – More computation needed when object closer
• Demo – hard to demonstrate but here goes
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Explanation of demo
• Created by combining two different views using a special camera – When focus behind (relax or defocus) you can reinstate
the slightly different views – Brain will then combine
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Monocular cues to depth
• Can perceive depth even with one eye – Based on experience in real world
• Size of retinal image
– In real world smaller images on retina mean object is further
– Can simulate this in two dimensions
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Retinal image as cue to depth
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Is the image of man in tie the same size?
With depth cues Without depth cues
Is the man in the blue shirt the same size in both images?
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Monocular cues to depth (cont’d)
• Texture gradients – More densely packed regions appear to be further
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Monocular cues to depth
• Linear perspective – lines in picture converge to a vanishing point
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Monocular cues to depth
• Interposition – one object blocking another
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Monocular cues to depth
• Motion parallax – when moving more distant objects move slower
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Summary of depth perception
• Depth is perceived (created by brain) – Not in stimulus
• Stimulus is 2-D image on retina
• Cues we use based on experience in real world • Both monocular and binocular cues
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Perceptual constancy
• Critical for maintaining constant perception of world
• Knowledge of world contributes to perception – Two people stand next to one another – One starts to move away – We do not perceive the moving person as getting
smaller
• Example of size constancy – Know that people don’t shrink – So perceive constant size – Despite change in size on
retina (image gets smaller as moves away)
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Example of shape constancy
• Image on retina changes as angle of opening changes – Still perceive door as same
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Illusions
• Use assumptions we make to fool us • Ames room example
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Explanation of Ames room
• Assumption is that room is rectangular
• Actual shape is trapezoid
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Perceptual organization
• Idea of perception – “what you see is NOT necessarily what you get”
• Perception based on
– Sensation – Knowledge and experience
• Understanding how we organize our world
– Visual experience not just series of action potential in rods and cones
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Gestalt Psychologists
• School lasted from 1920-1950 – Developed principles about how organize perception – Many still hold today
• Some Gestalt principles
– Principles of perceptual grouping – Figure ground relationships
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Perceptual grouping -similarity
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Perceptual grouping -principle of continuation
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Perceptual grouping - principle of proximity
• Is this organized in rows or columns?
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Perceptual grouping - principle of closure
• Complete stimuli to form objects
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Importance of figure-ground separation
• What is this a picture of ?
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Importance of figure-ground separation
• Importance of separating background and foreground
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Figure-ground confusions
• Ambiguous figures • No clear cues to
figure vs. ground
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Pattern recognition
• Bottom up theories – Pattern we see determined by features of object – Similar to idea of feature detectors
• Biederman’s Geon model
– Limited set of geons – Combine to form all objects
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Geons and pattern recognition
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Importance of context
• Context – surrounding elements, angle of viewing, motion – Things other than the stimulus itself
• Bottom-up theories predict same stimulus, same pattern – But not necessarily true – Importance of context
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Context – same stimulus different perception
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Effects of context – the moon illusion
• Moon illusion • Explanation of
moon illusion
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The importance of context
Viewed as is faces are similar
Rotated 180
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The importance of context
A giant bird with a little person in mouth or a man in a canoe being attacked by giant fish
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Motion as context
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Effects of context
• Context can make us see things that are not really in the stimulus – Maybe most powerful
effect of context
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Perception in infants
• Nature vs. nurture – Importance of learning for perception – Is there learning with sensation?
• Not all of one or the other • Some likely nature
– Binocular disparity • Some likely nurture
– Interposition, linear perspective
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Testing depth perception in infants The visual cliff
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Learning and perception
• Visual cliff – certain perceptual abilities learned • Cochlear implants
– Sensations are not speech – Can learn to interpret as speech
• Restored sight
– Blind – learn to identify object by touch – Operation to eliminate blindness – Will they be able to identify object by sight – Limitations on these studies
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Visual deprivation studies
• Normal kittens have neurons in occipital lobe respond to diagonal lines
• Effects of contact lenses that only allow kittens to see vertical and horizontal (not diagonal lines) – Remove prior to age of 3 months – Remove after age of 3 months
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Visual distortion studies
• Glasses that invert the world – Early effects – Later effects – Perceptual experience
• Video on inverted vision